Sound effect generating devices, which serve as equipment for enhancing an acoustic effect in vehicle passenger compartments (hereinafter referred to as ASC (ASC: Active Sound Control) devices) are known (see, for example, U.S. Patent Application Publication No. 2006/0215846, U.S. Pat. No. 5,635,903, and Japanese Laid-Open Patent Publication No. 2006-193002).
According to U.S. Patent Application Publication No. 2006/0215846, a plurality of reference signals (Sr1, Sr2, Sr3) depending on engine rotational frequency [Hz] are generated. After a predetermined gain correcting process is performed on the reference signals, the reference signals are combined into a control signal (Sc) for generating a sound effect. Then, a gain correcting process depending on a change [Hz/s] in the engine rotational frequency per unit time is performed on the control signal (see, for example, FIGS. 12 and 14 of the U.S. Patent Application Publication).
According to U.S. Pat. No. 5,635,903, pseudo-sound signals corresponding to vehicle operating states including starting, traveling, accelerating, and decelerating of an electric vehicle are generated, and levels of the pseudo-sound signals are changed depending on the level of ambient noise, in order to switch between volume levels of the pseudo-sounds (see, for example, the summary and claim 1 of the U.S. patent).
According to Japanese Laid-Open Patent Publication No. 2006-193002, a pseudo-engine sound is increased or decreased depending on sounds in the vehicle passenger compartment (see, for example, the summary and claim 1 of the Japanese Laid-Open Patent publication).